The present invention relates generally to ink jet heads used for pulsed droplet ink jet printers, often also referred to as drop-on-demand ink jet printers.
U.S. patent application Ser. No. 522,328, and Japanese Laid-Open Patent Applications No.60-90770 and No.62-56150 respectively disclose compact ink jet heads.
The ink jet head disclosed in U.S. patent application Ser. No. 522,328, proposed by this applicant, comprises, as shown in FIG. 1A, a passage plate 21, nozzles 23, a piezo-electric element 24, and stuffing material 25. The passage plate 21 is grooved to form passages 22 to which pressured ink is supplied, whereas the piezo-electric element 24 is grooved, so that adjacent operating parts (referred to as actuators hereinafter) thereof cannot come into contact with each other. Each nozzle 23 is attached to an outlet of each passage 22. Each groove in the piezo-electric element 24 is filled with the stuffing material 25 to prevent pressured ink from leaking into it. Each actuator is not flexed while not energized, as shown in FIG. 1A, whereas it is flexed, while energized, as shown in FIG. 1B, to generate a pulse each of the respective passages 22. Due to the flexure of the actuator, ink in the passage 22 is jetted via the nozzle 23. However, since each actuator heaves the adjacent stuffing material 25 and moves the passage plate 21 upwardly, as shown in FIG. 1B, the flexure force of the actuator does not sufficiently transmit to the passage 22 and thus sufficient ink is not jetted from the nozzle 23. This tendency becomes noticeable as a plurality of actuators are simultaneously energized.
The ink jet head disclosed in Japanese Laid-Open Patent Application No.60-90770 uses a piezo-electric strain constant with respect to a direction in which a piezo-electric element is polarized. The actuators are coupled to each other via a plate. However, due to the plate, this ink jet head has a disadvantage in that adjacent actuators interfere with each other during flexure thereof. The ink jet head disclosed in Japanese Laid-Open Patent Application No.62-56150 comprises a piezo-electric element having deep grooves and shallow grooves, and a passage plate which is not grooved. However, this ink jet head has a disadvantage in that it is difficult to form the deep and shallow grooves in piezo-electric element.
On the other hand, Japanese Laid-Open Utility Model Publications No.59-5570 and No. 58-30824 are directed toward the problem of bubbles in the passage. If the passage includes bubbles or does not include sufficient ink, sufficient ink cannot be jetted from the nozzle. In addition to not being able to completely print out all input data, the printer using the head cannot indicate the above condition as being an error. Accordingly, Japanese Utility Model Publication No.59-5570 discloses an ink jet head in which bubbles and insufficient ink in the passage can be detected. Japanese Utility Model Publication No. 58-30824 discloses an ink jet head in which bubbles in the passage can be removed. However, bubbles must be detected in each nozzle in a multinozzle head since each nozzle affects the image quality, and in a color printer, a number, defined by (four colors)*(the number of nozzles), of detecting circuits is needed, which makes the printer expensive. Moreover, since the conventional detecting circuit are located at the actuator to detect bubbles by means of a change in driving voltage, the detecting sensitivity is so bad that the detecting circuits can detect only a large amount of bubbles.